Control of static electrification by use of mixture brushes



cautionary steps must Patented Jan. 8, 1963 CONTROL OFSTATICELECTRIFICATEUN BY USE 9F MIXTURE BRUSHES Robert (Iunningharn and ThomasC. Whitmcre, Roch- This invention concerns the control of electrostatic'chargesand antistatic brushes which can be used for electrostaticcontrol. Electrostatic charges are very often built up due to thecontact or rubbing action of two materials. This can ;occur when anamber rod'is rubbed against a silkcloth for laboratory demonstrationpurposes and it can also occur in various commercial operations due tothe handling or conveying of products. In the photographic industry,electrostatic charges can be a serious problem :since the discharge ofstatic electricity results in static lines onsensitized photographicproducts making them unsuitable for general use. For this purpose,antistatic agents are often incorporated in the antihalation coating onthe back of photographic film. However, special prebe taken with much ofthe equipment which is used in connection with the manufacture 'ofphotographic elements, especially X-Ray film which sometimes does nothave an antistatic coating.

In the handling of sheetfilm having a photographic emulsion thereon, ithas been desirable to use a brush to push the film into place during thepackaging operation. This makes a neat stack of a given number of filmsheets and permits the stacks of film .to be wrapped with suitablepackaging material. These brushes should be long wearing, free fromadverse effect on photographic materials, relatively easy'to make orobtain, flexible, and relatively inexpensive.

Nylon brushes have been found to have the most satisfactorycharacteristics. However, the movement of a brush made from nylonagainst the edge of the photographic film results in the film having apronouncedelec: trostatic charge and the brush having a charge of-theopposite polarity. 'After a number of sheets have been brushed with thestacking brush, the electrostatic potential between the brush and thestack of film becomes large enough to cause a discharge or spark withthe resultant static marks on the photographic film. Accordingly, it hasbeen desirable to find a means of counteracting the tendency of the filmor the brush to pick of the static charge and to avoid damaging thesensitized film.

We have found that the static discharge between the brush and thephotographic film can be prevented by preparing a brush of specificchemical composition.

One object of this invention is to provide an antistatic material whichmay be used for brushes, rollers, and

the like. Another object is to provide an useful for packagingsensitized photographic film sheets. A further object is to provide amethod of making antistatic materials useful in handling photographicsheeting.

The above objects are obtained by combining two polymeric compositionsin a physical mixture or by combining bristles of different composition.A copolymer representing about 92 to 60 weight percent of vinylidenechloride and from 8 to 40 percent of .acrylonitrile (identified hereinas saran) is mixed with a polyhexamethylene diamine adipamide (66nylon), or polycaprolactam (6 nylon), both of which are intended by theterm nylon used herein.

The range of proportionsof nylon to saran by weight which can be used inour invention is 10 to 40 percent nylon with 90 to 60 percent saran.This refers to individual bristles made of a mixture of the polymers orto antistatic brush brushes which are substantially composed essentiallyof either nylon or saran. However, our preferred proportion is 85percent saran and 15 percent nylon. Some variation in the. physicalmixture proportions may be desired, depending upon the application forwhich the antistatic brushes ormaterials are intended.

In our preferredembodiment, bristles for the antistatic brushes areextruded fibers cut 1 /2 inches in length including the portion used toanchor them in the support but other lengths may be used. The diameterof the bristles depends on the volume by weight of the material used.However, the diameter of the bristles is preferably between 0.008 to0.017" averaging about 0.010".

In our preferred embodiment, brushes made according to our invention areused for packaging sheets of X-ray film. These brushes are made bymounting the bristles in a suitable mounting medium. In our preferredembodiment, the bristles are mounted in a steel support to providerigidity for the brush, .but the mounting medium could be nylon orsome-similar substantially rigid material, preferably one that isconductive so that the electrostatic charges which are induced in thebrush bristles would be readily dissipated.

The following examples are intended to illustrate our invention but arenot intended to limit it in any Way.

EXAMPLE 1 For testing the antistatic properties ofbrushes, a laboratory.testing device was constructed. A stack of X-ray film packets was placedon a grounded metal plate with apiece of cardboard inserted between theplate and the bottom of the packet. The metal plate was cut away so thatthe. brushes would not touch it and the X-ray film packets were held inplace on the plate using insulating (polystyrene) guide posts.Mechanical means were provided connected to a variablespeed motor sothat the .brushes could be used to brush against the edge of the filmpackets. A fieldmeter pick-up was mounted over the center of the stackto-record the potential generated on the stack. Sincethe film in thepackets extended beyond, the paper, the brushes were contacting bothpaper and film. Tests were made at two different brushing speeds,approximately one brush passage per second and two brushpassagespersecond. Tests were made also with .two. different amounts of overlap ofthe brush bristles on the stack and /2". Before testing, the brushmaterials and packets were conditioned overnight at F. to 50 percentrelative humidity. These conditions were maintained during the testingperiod. The

The above tests were run brushing the open end of the packet, twobrushes per second and with /z-inch brush overlap.

EXAMPLE 2 The following results were obtained brushing the open end ofthe packet with brushes containing either pure nylon or pure saran orbrushes containing bristles made completely of one or the other andintermixed in various proportions. The open end of the packet wasbrushed, two brushes per second, one-half inch overlap:

The following table gives values for tests run under the same conditionsas in Example 2 except that the closed end of the packet was brushed:

Table III Nylon, Saran, Field percent percent volts The above valuesindicate that brushes prepared according to our invention haveelectrical properties which compare favorably to metal bristles or metalcoated bristles but have essentially the flexibility, durability, etc.of nylon bristles.

The use of brushes which are composed essentially of nylon requires aspecial treatment. These nylon brushes must be soaked in a solution ofan antistatic agent. A suitable antistatic agent which can be used forthis purpose is identified as a cationic alkyl amine derivative.However, although this antistatic agent renders the brushes free fromobjectionable electrostatic charge, it is not a permanent treatment butwears off after a number of brushings over the photosensitive material.Therefore, the brushes must be frequently removed for retreating,necessitating additional time and expense which is avoided by the use ofbrushes made according to our invention.

Other antistatic agents which may be used for soaking brushes includesuch materials as triethanolarnineoleate, triethanolaminestearate, andthe like. Certain polymeric materials, such as polyalkylenepolyaminenucleus-containing polymers may also be used. These includepolyacrylyloxyalkyltrialkyl ammonium alkyl sulfate salts and the like.Certain phosphorous materials may be used such as a mixture ofdiethanolamine salts of phosphate esters, oxyalkyleneamine derivativesof phosphorous, and the like.

Although the conditions of treatment using the various antistatic agentsfor soaking brushes may be widely varied, we prefer to soak nylonbrushes in a 10 percent solution of a commercially available cationicalkylamine derivative.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention as described hereinabove and as defined in the appendedclaims.

a We claim:

1. An antistatic brush containing bristles made from a mixture comprisedof a polymer selected from the class consisting of polyhexamethylenediamine adipamide and polycaprolactam and a copolymer having 92 toweight percent of vinylidene chloride and from 8 to 40 percent ofacrylonitrile. I 2. An antistatic brush comprising bristles made from amixture comprised of 10 to 40 percent of a polymer selected from theclass consisting of polyhexamethylene diamine adipamide andpolycaprolactam and -60 perment of a copolymer containing 92 to 60weight percent of vinylidene chloride and from 8 to 40 percentacrylonitrile.

3. An antistatic brush for use in packaging photosensitive materialscomprising bristles made of a mixture comprised of a polymer selectedfrom the class consisting of polyhexamethylene diamine adipamide andpolycaprolactam and a copolymer of vinylidene chloride and.acrylonitrile.

References Cited in the file of this patent UNITED STATES PATENTS2,665,443 Simon et a1. Jan. 12, 1951 2,845,648 Peterson Aug. 5, 19582,851,735 Hogg et al. Sept. 16, 1958 2,970,884 Stanton et a1. Feb. 7,1961 FOREIGN PATENTS 505,769 Canada Sept. 14, 1954 723,023 Great BritainFeb. 2, 1955 1,055,749 Germany Apr, 23, 1959 OTHER REFERENCES AmericanDyestuif Reporter Antistatic Finishes for Textiles pp. 368371 (only p.368 relied on), June 7. 1954.

3. AN ANTISTATIC BRUSH FOR USE IN PACKAGING PHOTOSENSITIVE MATERIALSCOMPRISING BRISTLES MADE OF A MIXTURE COMPRISED OF A POLYMER SELECTEDFROM THE CLASS CONSISTING OF POLYHEXAMETHYLENE DIAMINE ADIPAMIDE ANDPOLYCAPROLACTAM AND A COPOLYMER OF VINYLIDENE CHLORIDE ANDACRYLONITRILE.